1. Field of the Invention
The present invention generally relates to an injector adapted for injecting ground hardening material in order to improve soft ground and prepare foundation of building site.
2. Description of the Prior Art
Conventionally, various ground hardening material injectors have been provided as shown in FIG. 8. In the drawing, (A) shows the oldest type injector which can inject only ground hardening material; and (B) shows a secondary old type injector which injects ground hardening material with effusing compressed gas such as air. But the type (B) could not overcome some defects, so that in recent years a type (C) injector provided with two injection nozzles has been broadly used. Its upper injection nozzle injects water and gas, and its lower injection nozzle injects only ground hardening material. In detail, the upper injection nozzle can inject the compressed water to a great distance by effusing gas around the water so that the compressed water can forcibly discharge liquid sludge towards the ground surface. This liquid sludge discharging effect has been known as "air lift effect". On the other hand, the lower injection nozzle does not inject gas and thus such air lift effect owing to cavitation by effusing gas can not be generated. Accordingly, the ground hardening material injected from the lower injection nozzle will be substituted for only the liquid sludge removed by the air lift effect by the upper injection nozzle. This means that the ground hardening material will not reach to required far distance and may flow upwardly to ground surface. This type (C) has provide poor displacement ratio; 1/2 or less, from ground to the ground hardening material.